Baffle structure for underwater transducer array

ABSTRACT

A frame supports a plurality of spherical transducers arranged in an array which combines sonic energy from the transducers into a beam pattern. The interstices between the transducers are filled with sealed capsules which increase stiffness and impedance to the passage of sound without greatly increasing the weight of the array.

United States Patent Massa Oct. 17,1972

1541 BAFFLE STRUCTURE FOR UNDERWATER TRANSDUCER ARRAY [72] inventor: Frank Massa, Cohasset, Mass.

[73] Assignee: Massa Division Dynamics Corporation of America, Hingham, Mass.

22 Filed: Aug. 5, 1910 [21] App1.No.: 61,198

Massa ..340/9 Tuttle ..340/9 Massa ..340/9 X [57] ABSTRACT A frame supports a plurality of spherical transducers [52] US. Cl. ..340/8 S, 310/9.l, 340/9 arranged in an array which combines sonic energy "601v from the transducers into a b pattern. h i 1 o catch 8 terstices between the transducers are filled with sealed 56 R d capsules which increase stiffness and impedance to the 1 e erences I e passage of sound without greatly increasing the weight UNITED STATES PATENTS of the y- 2,906,99l 9/1959 Camp ..340/9 X 8 Claims, 2 Drawing Figures l4 /3 /3 42 I4 /2 l a Q a l2 l 22 J J 14 Q 0 Q Q BAFFLE STRUCTURE FOR UNDERWATER TRANSDUCER ARRAY This invention relates to baffle structures and frame assembly for mounting spherical underwater transducers in an array having a configuration whereby a highpower directional source of sound can be realized.

A directional, low frequency, underwater acoustic source can be achieved by mounting a large number of individual transducers in an array configuration. The combined sonic radiation from the transducers in such a large array produces a desired source level and directional radiation pattern. For a conventional type of transducer (such as a vibratile piston diaphragm) sonic energy radiates from one side of a rigid housing. It is possible to assemble a group of such transducers into a large array with a configuration which achieves good acoustic coupling to an underwater environment without degradation in the radiation impedance of the array. U.S. Pat. No. 3,492,634, issued on Jan. 27, 1970, shows a typical array of such vibratile piston transducers.

Good acoustic coupling is realized, even for arrays comprising vibrating pistons of a circular shape, which may include unbaffled spaces between the vibrating piston surfaces. However, if transducers of the inertial type are mounted in such an array configuration, unbaffled spaces remain between the oscillating transducers. Then, there is a degradation in acoustic coupling within the array, since there is an interference between the out-of-phase radiations from the front and back surfaces of the vibrating transducer.

This invention describes a supporting structure for assembling an array of transducers and improving the acoustic coupling between them. Exemplary of the transducers which may realize a benefit from the array structure incorporating the teachings of this invention are those in which the complete outer transducer housing oscillates as a simple dipole element. Such a transducer may have a generally cylindrical shape as illustrated in U.S. Pat. No. 3,225,326 dated Dec. 21, 1965. The transducer may also have a spherical shape type, as shown in U.S. Pat. No. 3,319,220 dated May 9, 1967. When an array of inertially driven spherical transducers is to be assembled, the spaces between the mounted transducer elements may give rise to lowered radiation efficiency because there is an acoustic interference through the interstices between the transducers. An out-of-phase radiation occurs responsive to sound radiated from the front and back surfaces of the oscillating spheres.

One obvious means for preventing this interference or interaction between the out-of-phase radiations from the front and back surfaces is to use massive solid plugs to fill the spaces between the transducers in the array. For this solution to the problems, the plugs must have a substantial weight, especially if they are to be effective at the lower frequencies. The inertial reactance of the plugs is high compared with the radiation impedance of the water surrounding the plugs. Therefore, this use of massive plugs is an impractical method of increasing the front-to-back impedance through the interstitial openings between the transducers in the array. The method becomes even more impractical for low frequency applications, because the weight of the plugs adds considerable to the weight of the entire array frame assembly.

Accordingly, an object of this invention is to provide a baffle structure for mounting an array of inertiallydriven spherical transducers for improving radiation efficiency.

Another object of this invention is to provide an array frame comprising a rigid assembly of tubular mounting structures contiguously positioned with their center axes parallel in an adjacent side-by-side configuration. Another object is to utilize the stiffness reactance of hollow capsules which are rigidly attached to the outside walls of tubular structures to bridge the spaces between the tubular sections.

A still further object of this invention is to provide a generally rectangular frame structure including a number of tubular sleeve sections rigidly attached to each other and to the frame in order to form a rectangular array of circular tubular openings with the axes of said tubular openings lying generally perpendicular to the plane of the frame structure.

A still further object of this invention is to provide a relatively lightweight frame and baffle structure for assembling low frequency underwater inertial transducers into a predetermined array.

In keeping with an aspect of this invention, these and other objects are accomplished by a use of lightweight sealed capsules which completely fill the interstices between the mounted transducers. These capsules achieve the desired objective by providing a high stiffness reactance, rather than a high mass reactance, for increasing the front-to-back impedance through the interstices between the transducers.

The novel features which are characteristic of the invention are set forth with particularity in the appended claims.

However, the invention itself, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of an array structure illustrating one embodiment of this invention; and

FIG. 2 is a cross section view taken along line 2-2 of FIG. 1. g

In greater detail, a rectangular frame 11 may include welded steel channels, for example, which form the main support for the structure. These channels hold a welded cluster of nine circular steel sleeve mounting structures 12 which are arranged in the form of a 3 33 3 array. Although this particular array is here illustrated with nine tubular elements arranged in a square configuration, it should be understood that any other combination of elements may also be used according to the needs of a particular application.

Each of the tubular elements 12 includes a plurality of mounting brackets 13 welded to their peripheries. These brackets provide means for attaching the transducer structures which are to be assembled within the tubular openings For example, a suitable transducer mounting structure uses spherical transducers 20 having equatorial elastomer belts 21 which are compressingly forced, with an interference fit, into the cylindrical openings of the array structure of FIG. 1. Each belt has a number of undercut slots, as at 22, which allow cooling water to reach the transducer housing. An example of such a transducer is found in my copending application Ser. No 60,258, filed Aug. 3, 1970, entitled MOUNTING STRUCTURE FOR SPHERICAL SHAPED UNDERWATER TRANSDU- CER, and assigned to the assignee of this invention.

Hollow stiff-walled capsule members 14 and 15 are assembled inside the interstitial spaces between the adjacent outer peripheries of the rigidly assembled circular sleeves 12. The capsule 15 is shown in cross section in FIG. 2. Each capsule consists essentially of a cylindrically shaped tubular body with hemispherical end caps welded thereto. The capsule 14, shown in cross section in FIG. 2, consists essentially of a one-half section of the capsule 15. These half section capsules fit into the spaces between the outer rows of the sleeves 12 and the adjacent flat surfaces of the frame structure 11. The capsules 15 are welded to four surrounding walls of the circular sleeves 12 wherever they come together throughout the array. Similarly, the capsules 14 are welded to the two adjacent cylindrical sleeve structures that come together at the frame, and they are also welded to the face of the frame 11.

These hollow capsules 14, 15 fill the interstices between the tubular members 12. They provide a high degree of stiffness reactance for increasing the front-toback impedance to passage of sonic energy through the interstices. Thus, there is a high acoustic impedance to prevent passage of interfering, out-of-phase acoustic energy from the back to the front of the array, when transducer elements are mounted within the openings of the tubular members 12, for acoustic operation of assembled array.

Thus, the hollow capsules 14 and 15 impede the circulation of the out-of-phase sound between opposite sides of the transducers in the array. The weight is greatly reduced as compared with the weight that would be required if the interstices were filled with massive solid plugs. If, in place of the hollow stiff capsules, stiff circular plates were welded into the interstices, such plates would act as transmission lines. The low frequency underwater sound vibrations would be transmitted directly through these stiff plates almost as if they were not present. Therefore, the plates would be ineffective for improving the radiation efficiency of the array.

This invention has been described in connection with an illustrative embodiment of the basic idea. However, numerous deviations are possible. Therefore, the description of the invention and the appended claims should be construed to include all equivalent structures.

lclaim:

l. A supporting structure for holding an array of unmemb rs are sealed hollow housin tructures 3. The invention in claim 2 whei e in each of said hollow housing structures comprises a cylindrical body section which is sealed at each end of said cylinder.

4. The invention in claim 2 wherein said capsule members are substantially hollow spheres.

5. The invention in claim 1 and mounting means comprising brackets attached about the peripheries of said tubular members, said brackets being in the interstitial regions of the assembled array structure.

6. A supporting structure for holding an array of underwater transducers, said structure comprising a frame member, a plurality of contiguously positioned rigid tubular members with their axes parallel, said tubes having circular cross sections with interstitial spaces between said circular sections, means for rigidly holding said plurality of rigid tubular members in a fixed array pattern within said frame member, a plurality of stiff capsule members, and means for rigidly hold ing said capsule members within the interstitial spaces between said tubular members, wherein each of said transducers comprises a spherical dipole structure having an equatorial elastomer belt, said transducers being pressed into individually associated ones of said tubular members with said elastomer belt having an interference fit between the tube and sphere.

7. The invention in claim 1 further characterized in that the stiffness reactance of said capsule member is greater than the radiation impedance of the medium in contact with the surface of said capsule, said impedance being at the frequency of operation of the array.

8. A frame structure comprising means for holding an array of transducers with at least one working surface of each transducer exposed to a surrounding medium, said frame and transducer structure having interstitial openings therein, and baffle means having a stiffness reaction filling said interstitial openings, the impedance to sonic radiation at the transducer operating frequency being greater in said baffle means than in said surrounding medium. 

1. A supporting structure for holding an array of underwater transducers, said structure comprising a frame member, a plurality of contiguously positioned rigid tubular members with their axes parallel, said tubes having circular cross sections with interstitial spaces between said circular sections, means for rigidly holding said plurality of rigid tubular members in a fixed array pattern within said frame member, a plurality of stiff capsule members, and means for rigidly holding said capsule members within the interstitial spaces between said tubular members.
 2. The invention in claim 1 wherein said stiff capsule members are sealed hollow housing structures.
 3. The invention in claim 2 wherein each of said hollow housing structures comprises a cylindrical body section which is sealed at each end of said cylinder.
 4. The invention in claim 2 wherein said capsule members are substantially hollow spheres.
 5. The invention in claim 1 and mounting means comprising brackets attached about the peripheries of said tubular members, said brackets being in the interstitial regions of the assembled array structure.
 6. A supporting structure for holding an array of underwater transducers, said structure comprising a frame member, a plurality of contiguously positioned rigid tubular members with their axes parallel, said tubes having circular cross sections with interstitial spaces between said circular sections, means for rigidly holding said plurality of rigid tubular members in a fixed array pattern within said frame member, a plurality of stiff capsule members, and means for rigidly holding said capsule members within the interstitial spaces between said tubular members, wherein each of said transducers comprises a spherical dipole structure having an equatorial elastomer belt, said transducers being pressed into individually associaTed ones of said tubular members with said elastomer belt having an interference fit between the tube and sphere.
 7. The invention in claim 1 further characterized in that the stiffness reactance of said capsule member is greater than the radiation impedance of the medium in contact with the surface of said capsule, said impedance being at the frequency of operation of the array.
 8. A frame structure comprising means for holding an array of transducers with at least one working surface of each transducer exposed to a surrounding medium, said frame and transducer structure having interstitial openings therein, and baffle means having a stiffness reaction filling said interstitial openings, the impedance to sonic radiation at the transducer operating frequency being greater in said baffle means than in said surrounding medium. 